Substrate temperature control apparatus and technique for CVD reactors

ABSTRACT

One of the critical experimental parameters affecting the quality and  gro rate of chemical vapor deposition species, such as, diamond is the substrate temperature. An apparatus and technique for the precise control of the substrate temperature in a chemical vapor deposition environment has been developed. In a preferred embodiment, the technique uses a variable gas mixture in conjunction with the disclosed apparatus of the present invention to precisely control the temperature of the substrate to within at least ±20° C. for extended periods of time and over large area substrates on the order of 1&#34; in diameter or larger.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to high heat load processes, forexample, chemical vapor deposition (CVD) and more specifically to anapparatus for precisely controlling the temperature of a substrateduring such high heat load processes.

2. Description of the Related Art

The current interest in chemical vapor deposition (CVD) of diamond canbe traced to work in the early 1980's which showed that activating ahydrogen-hydrocarbon mixture with a hot filament could generate diamondgrowth rates in the 1 μm/hr range. Today, growth rates for opticalquality diamond films are about 2-4 μm/hr. At such growth rates,fabrication of bulk diamond windows on the order of 10 cm in diameterand 1 mm thick can require greater than 500 hours or nearly 21 days.

Most CVD processes occur at high temperatures on the order of about200°-2000° C. CVD processes include oxygen-acetylene flame CVDprocesses, atmospheric pressure plasma CVD processes, lower heat fluxCVD processes, microwave assisted CVD processes and filament assistedCVD processes. In the field of diamond growth by flame CVD, for example,a diamond substrate or a non-diamond substrate is held within anoxygen-acetylene flame in order to promote the deposition of diamond onthe substrate in a hydrogen and hydrocarbon rich atmosphere. Thetemperature of the substrate is regulated between 200°-2000° C. whilethe diamond grows during the CVD process. Typically, the substratetemperature is difficult to control with precision. Due to the high heatloads used, for example, in excess of 1 kW/cm², it is difficult tocontrol with precision the temperatures between 200°-2000° C. at thesubstrate or at the substrate mount and it is difficult to prevent thesubstrate from overheating. The lack of precise temperature control atthe substrate or at the substrate mount during high heat load processessuch as the chemical vapor deposition of, for example, diamond is due toa deficiency in the control over thermal heat conduction carrying heataway from the substrate attached to the substrate mount.

One of the critical experimental parameters affecting the quality, forexample, the growth of graphite instead of diamond, is the substratetemperature, which, in the case of homoepitaxy, is the seed crystaltemperature. In CVD processes, a substrate mount rod with a pre-attacheddiamond substrate, seed crystal diamond substrate or non-diamondsubstrate may be used. Alternatively, no such pre-attached substratemount need be used, in which case, the bare upper surface of thesubstrate mount rod is itself referred to as the substrate. Most CVDreactors operate between 200°-2000° C., wherein such high heat loadsrequire active cooling of the substrate in order to maintain a desiredtemperature. The substrate temperature can be adjusted by varying theCVD reactor's power level; however, varying the power level tends tochange the gas phase deposition chemistry within the reactor, thusaltering the growth conditions and the material properties of thediamond grown.

Changing the coolant flow rate to the substrate mount housing (the heatsink) does not give much dynamic precision control over the desiredtemperature range, especially in high growth rate processes employing anoxygen-acetylene torch or an atmospheric pressure plasma torch. Nor doesthe use of other types of heat sinks provide any better precisioncontrol of the substrate temperature. Other types of heat sinks includespray coolers, closed loop heat transfer oil systems and heat pipeswhich can all be substituted for a fluid cooled substrate mount housing,for example, a water cooled copper housing. While several groups havetried inserting thermal resistors between a water cooled housing(substrate mount holder) and the substrate mount, such an apparatus doesnot provide dynamic precision control during high heat load processessuch as CVD. In addition, such techniques do not provide precisiontemperature control with uniformity over large area substrates.

With the substrate attached to a molybdenum rod (substrate mount), amolybdenum rod threaded into a water cooled housing (substrate mountholder) has been used to control the temperature at the substrate duringCVD. The rod can be screwed into or out of the water cooled housing asneeded to control the magnitude of heat transfer away from thesubstrate, which, in turn, controls the temperature of the substrateduring CVD. While varying the degree of exposure of the molybdenum rodout of the water cooled housing alters the resistance of the thermalpathway between the substrate and the water cooled housing, thistechnique cannot control substrate temperature with precision or controlsubstrate temperature with uniformity over a large area substrate. Thistechnique uses the mechanical motion of an object (substrate mount rod),typically, at 900°-1400° C., wherein precise temperature control isdifficult to maintain. For example, after about one hour of growth inair, using a threaded molybdenum rod as a substrate mount rod, themolybdenum oxidizes to molybdenum oxide on the rod's threads.Subsequently, it becomes difficult or impossible to rotate themolybdenum rod either into or out of the water cooled housing. As aresult, the temperature of the substrate and the substrate mount cannotbe controlled with the precision desired.

SUMMARY OF THE INVENTION

It is therefore an object of the claimed invention to control substratetemperature with precision during high heat load processes, for example,chemical vapor deposition, independent of a CVD reactor's power level.

It is another object of the present invention to reliably controlsubstrate temperature with precision during high heat load processes,for example, chemical vapor deposition, over extended periods of time.

It is yet another object of the present invention to uniformly controlthe substrate temperature during high heat load processes over largearea plate-shaped substrates.

These and other objects are achieved by the use of an apparatus in whicha gas or a gas mixture is flowed to the heat sink in a space between thesubstrate mount and a heat sink to promote the transfer of heat from thesubstrate and substrate mount.

These and other objects and advantages of the invention may be readilyascertained by referring to the following detailed description andexamples of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and several of theaccompanying advantages thereof will be readily obtained by reference tothe following detailed description when considered in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a vertical cross-sectional view of an apparatus representativeof a first preferred embodiment according to the present invention.

FIG. 2 is another preferred embodiment of the present invention.

FIG. 3 is a cross-sectional view taken along the line 3--3 of theembodiment shown in FIG. 2.

FIG. 4 is a plot of the molybdenum mount rod (substrate mount)temperature (°C.) versus helium (He) gas fraction using the firstpreferred embodiment of the present invention (apparatus of FIG. 1)wherein total gases consist of helium (He) and argon (Ar) and total gasflow rate was 200 sccm (standard cm³ /minute) through the threadedinterface between the water cooled housing (substrate mount holder) andthe molybdenum rod (substrate mount) and wherein the number of threadsexposed above the water cooled housing are indicated.

FIG. 5 is a plot of the molybdenum mount plate (substrate mount)temperature (°C.) versus helium (He) gas fraction using the secondpreferred embodiment of the present invention (apparatus of FIG. 3)wherein total gases consist of helium (He) and argon (Ar) and total gasflow rate was 200 sccm (standard cm³ /minute) through the threadedinterface between the water cooled housing (substrate mount holder) andthe molybdenum plate (substrate mount).

FIG. 6 is another plot of the molybdenum mount rod temperature (°C.)versus helium (He) gas fraction using the first preferred embodiment ofthe present invention (apparatus of FIG. 1) wherein total gases consistof helium (He) and argon (Ar) and total flow rate was 200 sccm (standardcm³ /minute) through the threaded interface between the water cooledhousing (substrate mount holder) and the molybdenum rod (substratemount).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description of the preferred embodiments isprovided to aid those skilled in the art in practicing the presentinvention. However, the following detailed description of the preferredembodiment should not be construed to unduly limit the presentinvention. Variations and modification in the embodiments discussed maybe made by those of ordinary skill in the art without departing from thescope of the present invention.

FIG. 1 shows a vertical cross-sectional view of an apparatus for thesynthesis of, for example, diamond via chemical vapor deposition on asubstrate seed crystal 10 (optional) attached to a substrate mount rod12, in this case made of molybdenum. In the case of non-homoepitaxialgrowth, no additional substrate 10 need be pre-attached to the substratemount rod 12. In such a case, the bare upper surface 24 of the substratemount rod 12 also serves as substrate. To initiate chemical vapordeposition growth, a substrate seed crystal 10 may be attached to thesubstrate mount rod 12 via, typically, an appropriate brazing material.Alternatively, diamond can be directly grown, for example by CVD, on thebare substrate mount rod upper surface without using a pre-attached seedcrystal.

FIG. 2 shows a vertical cross-sectional view of an second preferredembodiment of an apparatus for the synthesis of, for example, diamondvia chemical vapor deposition on a substrate seed crystal 40 (optional)attached to a substrate mount disk 42, in this case made of molybdenum.In the case of non-homoepitaxial growth, no additional substrate 40 needbe pre-attached to the substrate mount disk 42. In such a case, the bareupper surface 44 of the substrate mount disk 42 also serves assubstrate. To initiate chemical vapor deposition growth, a substrateseed crystal may be attached to the substrate mount disk 42 via,typically, an appropriate brazing material. Alternatively, diamond canbe grown, for example by CVD, on the bare substrate mount disk uppersurface without using a pre-attached seed crystal.

The substrate mount rod 12 (FIG. 1) or substrate mount disk 42 (FIG. 2)may be made from materials that have melting points above thetemperatures at which chemical vapor deposition of the depositionspecies, for example, diamond is carried out. Generally such materialsshould be stable between 200°-2000° C. The materials selected from whichthe substrate mount rod 12 (FIG. 1) or substrate mount disk 42 (FIG. 2)are manufactured are those that have thermal conductivities which allowthe temperature at the substrate to be precisely controlled betweenabout 200°-2000° C. as desired. Precision temperature control to atleast about ±20° C., about ±10° C., about ±5° C., about ±2° C., andabout ±1° C. between about 200°-2000° C. has been achieved with thepresent invention.

In the first and second preferred embodiments, the materials from whichthe substrate mount rod 12 (FIG. 1) or the substrate mount disk 42 (FIG.2) may be manufactured, typically, have a thermal conductivity of about0.05-32 W/cm-°K. at 273° K. The intermediate and preferred ranges forthe thermal conductivity of materials from which the substrate mount rod12 (FIG. 1) or substrate mount disk 42 (FIG. 2) may be manufactured areabout 0.6-32 W/cm-°K. and about 1.0-32 W/cm-°K., respectively, at 273°K. The substrate mount rod 12 or substrate mount disk 42 (FIG. 2) istypically made of a refractory material. Suitable refractory materialsinclude, for example, graphite, molybdenum, sapphire, diamond, alumina,tungsten, titanium, niobium, beryllium oxide and mixtures thereof.

The substrate mount rod 12, in the first preferred embodiment, extendsthrough a heat sink made of a thermally conductive material 14. Thesubstrate mount disk 42, in the second preferred embodiment, is laidinto a cavity cut within the heat sink 56 as shown in FIG. 2. In thefirst preferred embodiment, the substrate mount rod 12 is threaded intothe heat sink 14. The upper surface 24 of the substrate mount rod 12(FIG. 1) or the upper surface 44 of the substrate mount disk 42 (FIG. 2)is the surface upon which the deposition species is grown or upon whicha seed crystal is pre-attached to the upper surface 24 of substratemount rod 12 (FIG. 1) or to upper surface 44 of substrate mount disk 42(FIG. 2) via an appropriate brazing material. The lower surface 26 ofthe substrate mount rod 12 (FIG. 1) or lower surface 46 of substratemount disk 42 (FIG. 2) is connected to a tube 28 (FIG. 1) or tube 48(FIG. 2) connected to one or more tanks, for example, 16 and 18,containing one or more gases, for example, 20 and 22, respectively.

Referring to FIG. 1, during, for example, the chemical vapor depositionof the deposition species onto substrate 10 or directly onto the uppersurface 24 or onto a seed crystal, the temperature of the upper surfaceof the substrate must be controlled with precision between about200°-2000° C. In order to maintain precision control of the temperatureof the substrate being subjected to high heat load from, for example,flame 30 during CVD, pressurized tanks (e.g. 16 and 18) release one ormore gases, for example, 20 and 22, into tube 28. If two or more gasesare used, then they mix as they flow through tube 28 toward the lowersurface 26 of the substrate mount rod 12. For the sake of convenience,the present invention is described here with respect to the use of amixed gas flow, it being understood that a single gas may instead beused. The mixed gases flow from tanks 16 and 18 into tube 28 through thethreaded gap interface 32 between the substrate mount rod 12 and theheat sink 14. The mixed gases flow from the lower surface 26 of thesubstrate mount rod 12 towards the upper surface 24. The mixed gasesflow through the threaded gap interface 32 and exit at the upper surface24 into, for example, the CVD chamber depicted in FIG. 1. The gas flowthrough the threaded gap interface 32 carries heat away from thesubstrate mount rod 12 and the substrate. This removal of heat from thesubstrate via the one or more gases, for example, 20 and 22, preciselycontrols the substrate temperature during high heat load processes whereheat loads in excess of 1 kW/cm² are commonly used, such as CVD.Preferably, a gas mixture contains one gas with a higher thermalconductivity than the other gas or gases. The thermal conductivities ofvarious gases are given below:

    ______________________________________                                        Thermal Conductivity of Gases at 50° C.                                       (Cal/cm-s-°C.) × 10.sup.-6                                                     (W/cm-°K) × 10.sup.-6                       ______________________________________                                        Nitrogen 65.7            274.9                                                Argon    45.5            190.4                                                Helium   376             1573                                                 Hydrogen 471             1971                                                 ______________________________________                                    

When two or more gases are used, one with a high thermal conductivityrelative to the other gases, one can vary the fraction of one gas to theothers to obtain precise temperature control over a temperature rangesufficient for growing diamond. For example, FIG. 4 and FIG. 6illustrate the dependence of the temperature of the substrate mount rod12 (or substrate mount disk, FIG. 5) on the helium gas fraction whereintotal gases were helium and argon, in an oxygen-acetylene flame CVDreactor. From FIGS. 4, 5 and 6 it should be noted that as the gasfraction of the gas with the larger thermal conductivity, for example,helium, is increased, the temperature of the substrate isproportionately lowered. The temperature dependence of the substrate onthe gas fraction of the gas with the larger thermal conductivity is acritical element of a preferred embodiment of the present invention. Theprecision temperature control is achieved not only by the choosing theright combination of gases but also by varying the gas fraction withinthe gas mixture.

In addition, the one or more gases selected, for example, 20 and 22, aregases which do not alter the growth chemistry of the desired depositionspecies, for example, diamond, between about 200°-2000° C. and do notreact with or oxidize the substrate mount rod 12 material, the heat sink14, and the tube material 28 sufficiently to obstruct the gas flowchannel terminating at surface 24. Any one or more gases may be usedwhich, in addition to the aforementioned non-reactivity, have sufficientthermal conductivity to allow precision temperature control of at leastabout ±20° C. of the substrate over a temperature of about 200°-2000° C.

In a preferred embodiment, the present invention uses a variable gasmixture of two or more gases passed through the threaded gap interface32 to control the heat transfer between the substrate mount rod 12 andthe heat sink 14. Any combination of gases may be used that issufficiently non-reactive with tube 28, the substrate 10, the substratemount rod 12, and the heat sink 14 and which allow precision temperaturecontrol of at least about ±20° C. of a substrate during a high heat loadprocess such as CVD between about 200°-2000 ° C. Preferably, the two ormore gases, for example, 20 and 22, are selected from the groupconsisting of argon, krypton, neon, carbon dioxide, helium, xenon andmixtures thereof.

The two or more gases released from tanks 16 and 18 into tube 28 andwhich flow through the threaded gap interface 32, exiting at the uppersurface 24, flow at a rate sufficient to control the temperature of thesubstrate with the precision of at least about ±20° C. over atemperature of 200°-2000° C. The data plotted in FIG. 4, FIG. 5 and FIG.6 was obtained wherein total gas flow rates were 200 standard cubiccentimeters per minute (sccm) for each plot, respectively. While theoverall size of the apparatus is determinative of the maximum gas flowrate that the apparatus can withstand, it is expected that a total gasflow rate from between about 10-1000 sccm is preferable for use in thepresent invention. In addition, while a helical threaded gap interface32 is used in the first preferred embodiment illustrated in FIG. 1, theexact shape of the gap interface is not critical. Nevertheless, the gapinterface should be of a sufficient size and shape to flow a gas orgases to obtain precision temperature control of the substrate of atleast about ±20° C. between about 200°-2000° C. For example, a helicalgap interface, a planar spiral gap interface, or a planar gap interfacemay be used.

In FIG. 1, the heat sink 14 is further cooled using a cooled liquidwhich flows through an internal cavity 38 within said heat sink 14. Athermally conductive fluid enters the internal cavity 38 of the heatsink 14 through inlet 34 and exits out of the cavity 38 through outlet36. The fluid absorbs heat from the heat sink 14. The temperature of theheat sink 14 can be controlled by a thermally conductive cooling fluid,for example, chilled water or water at room temperature.

The heat sink 14 may be made of any material that dissipates heat at arate which maintains the substrate at a desired temperature with theprecision of about ±20° C. between 200°-2000° C. during high heat loadprocesses. Typically, the heat sink 14 has a heat capacity, C_(p) °(Joules/deg-mol), between about 15-50 Joules/deg-mol at 273.15° K. Theintermediate and preferred ranges for the thermal conductivity of theheat sink 14 suitable for the present invention are about 1-5 W/cm-°K.and about 2-4.5 W/cm-°K., respectively, at 273° K. In addition, the heatsink 14 should be stable and unreactive with the gas or gases passedthrough the threaded gap interface 32, between about 15°-600° C. Forexample, the preferred heat sink 14 can be a copper heat sink with aheat capacity, C_(p) °, of 24.13 Joules/deg-mol at 273.15 ° C. and athermal conductivity of 4.01 W/cm-°K. at 273° K.

The thermally conductive fluid is any fluid that dissipates heat at arate which maintains the substrate temperature with the precision of atleast about ±20° C. between 200°-2000° C. Typically, the thermallyconductive fluid is any fluid that does not react with the heat sink 14between about 15°-300° C. and has a heat capacity or thermal capacity,C_(p) ° (Joules/deg-mol), of between about 3-5 Joules/deg-mol at 273° K.For example, the preferred thermally conductive fluid can be water witha thermal capacity of 4.2177 Joules/deg-gm at 273° K.

In addition to the aforementioned, the temperature of the substrate 10can be controlled by the number of threads of the substrate mount rod 12that are exposed out of the heat sink 14 nearest the flame 30. FIG. 4 isa graph of the substrate mount rod temperature as a function of thehelium gas fraction wherein total gases were helium and argon, whereintotal gas flow rate was 200 standard cm³, and wherein the number ofthreads exposed nearest the flame 30 (See FIG. 1) are varied from 1 to 3to 6 as indicated.

EXAMPLE 1

The layout used for controlling the temperature of the substrate mountrod 12 in a combustion assisted CVD system is described below. Theprecision control of the temperature of the substrate mount rod 12(depicted in FIG. 1) achieved is demonstrated by the data obtained fromsuch a system and disclosed in FIG. 4 and FIG. 6. In obtaining the datapresented in FIG. 4 and FIG. 6, the one or more gases used were heliumand argon. The total helium and argon gas mixture flow rate wascontrolled by two mass flow controllers (MKS model 1159) with the totalflow rate fixed at 200 sccm. A small outer diameter (0.125") copper tube28 was attached to two mass flow controllers. The gas mixture of heliumand argon was injected into the copper tube 28 which was attached to apressure fitting with an O-ring seal for a regular screwdriver. Thepressure fitting connected the copper tube 28 to the molybdenumsubstrate mount rod 12. A screwdriver was used to adjust the degree ofpenetration of the molybdenum substrate mount rod 12 (3/8-24 threadedrod, 0.5" long) into the copper heat sink 14 which was water cooled andapproximately 3" in diameter and 1.5" thick. The gas mixture wasreleased from tanks 16 and 18 into tube 28 and passed through thepressure fitting into the threaded gap interface 32 sandwiched betweenthe substrate mount rod 12 and the heat sink 14 at a constant total flowrate of 200 sccm. The individual flow rates of helium and argon werevaried to alter the gas fraction of helium released from 0 to 1. Whilethe total gas flow rate was held constant at 200 sccm, variation in thegas fraction of helium (in the mixture of helium and argon) resulted inthe ability to control the temperature of the substrate mount rod 12 towithin ±1°-2° C. The temperature of the substrate mount rod 12 wasmeasured by a two color pyrometer (Williamson model 8100) which isinsensitive to the flame emissions of the CVD reactor. By using aMacintosh IIx computer with the Lab View software package (NationalInstruments) a feedback control loop was used to maintain thetemperature of the substrate mount rod 12. The results of this exampleare plotted in FIG. 4 and FIG. 6 wherein substrate mount rod 12temperature is plotted against helium gas fraction wherein total gasflow rate was 200 sccm and total gases were helium and argon. Inaddition, the heat load in the CVD reactor was from an oxygen-acetyleneflame generated with a No. 4 welder's tip in which the oxygen andacetylene gas flow rates were 10.9 and 9.06 standard liters per minute(slm), respectively.

EXAMPLE 2

Another layout used for controlling the temperature of the substratemount disk 42 in a combustion assisted CVD system is described below.The precision control of the temperature of the substrate mount disk 42(depicted in FIG. 2) achieved is demonstrated by the data obtained fromsuch a system and disclosed in FIG. 5. In obtaining the data presentedin FIG. 5, the one or more gases used were helium and argon. The totalhelium and argon gas mixture flow rate was controlled by two mass flowcontrollers (MKS model 1159) with the total flow rate fixed at 200 sccm.A small outer diameter (0.125") copper tube 48 was attached to two massflow controllers. The gas mixture of helium and argon was injected intothe copper tube 48 which was attached to a pressure fitting with anO-ring seal. The pressure fitting connected the copper tube 48 to themolybdenum substrate mount disk 42. The molybdenum substrate mount disk42 had a diameter of 1" and a thickness of 5/16". In addition, a gapinterface channel between the heat sink 44 and the substrate mount disk42 is carved out on the underside of the substrate mount disk 42 in theshape of a planar spiral as shown in FIG. 3 and referred to as 52.Though not shown, the remainder of the apparatus is the same as thatdepicted in FIG. 1. As in FIG. 1, the gas mixture was released fromtanks 16 and 18 into tube 48 and passed through the pressure fittinginto the spiral gap interface 52 sandwiched between the substrate mountdisk 42 and the heat sink 44 at a constant total flow rate of 200 sccm.The individual flow rates of helium and argon were varied to alter thegas fraction of helium released from 0 to 1. While the total gas flowrate was held constant at 200 sccm, variation in the gas fraction ofhelium (in the mixture of helium and argon) resulted in the ability tocontrol the temperature of the substrate mount disk 42 to within ±1-2°C. The temperature of the substrate mount disk 42 was measured by a twocolor pyrometer (Williamson model 8100) which is insensitive to theflame emissions of the CVD reactor. By using a Macintosh IIx computerwith the Lab View software package (National Instruments) a feedbackcontrol loop was used to maintain the temperature of the substrate mountdisk 42. The results ()f this example are plotted in FIG. 5 whereinsubstrate mount disk 42 temperature is plotted against helium gasfraction wherein total gas flow rate was 200 sccm and total gases werehelium and argon. In addition, the heat load in the CVD reactor was froman oxygen-acetylene flame generated with a No. 4 welder's tip in whichthe oxygen and acetylene gas flow rates were 10.0 and 9.19 standardliters per minute (slm), respectively.

What is claimed is:
 1. A method for controlling the temperature of asubstrate having a growth surface during chemical vapor depositioncomprising the steps of:flowing two or more gases, through a gapinterface between a substrate mount for supporting said substrate and aheat sink; and varying the flow rate of one or more of said gasesflowing through said gap interface to control said temperature of saidgrowth surface of said substrate to a precision of at least about ±20°C. within a temperature range of about 200°-2000° C.
 2. The method ofclaim 1, whereinsaid step of varying said flow rate further comprisesvarying the flow rate of one or more of said gases to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±10° C. within said temperature range.
 3. The method ofclaim 1, whereinsaid step of varying said flow rate further comprisesvarying the flow rate of one or more of said gases to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±5° C. within said temperature range.
 4. The method ofclaim 2, whereinsaid step of varying said flow rate further comprisesvarying the flow rate of one or more of said gases to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±2° C. within said temperature range.
 5. The method ofclaim 1, whereinsaid step of varying said flow rate further comprisesvarying the flow rate of one or more of said gases to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±1° C. within said temperature range.
 6. The method ofclaim 2, whereinsaid step of varying said flow rate further comprisesvarying the flow rate of one or more of said gases to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±1° C. within said temperature range in response to afeedback temperature sensor.
 7. A method for controlling the temperatureof a substrate having a growth surface during chemical vapor depositioncomprising the steps of:flowing two or more gases, each of said gaseshaving a mole fraction, through a gap interface between a substratemount for supporting said substrate and a heat sink; and varying saidmole fraction of one or more of said gases flowing through said gapinterface to control said temperature of said growth surface of saidsubstrate to a precision of at least about ±20° C. within a temperaturerange of about 200°-2000° C.
 8. A method of claim 7 whereinsaid step ofvarying said mole fraction further comprises varying the mole fractionof one or more of said gases to control said temperature of said growthsurface of said substrate to a precision of at least about ±10° C.within said temperature range.
 9. A method of claim 7 whereinsaid stepof varying said mole fraction further comprises varying the molefraction of one or more of said gases to control said temperature ofsaid growth surface of said substrate to a precision of at least about±5° C. within said temperature range.
 10. A method of claim 7whereinsaid step of varying said mole fraction further comprises varyingthe mole fraction of one or more of said gases to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±2° C. within said temperature range.
 11. A method ofclaim 7 whereinsaid step of varying said mole fraction further comprisesvarying the mole fraction of one or more of said gases to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±1° C. within said temperature range.
 12. A method ofclaim 7 whereinsaid step of varying said mole fraction further comprisesvarying the mole fraction of one or more of said gases to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±1° C. within said temperature range in response to atemperature feedback sensor.
 13. A method for controlling thetemperature of a substrate having a growth surface during chemical vapordeposition comprising the steps of:flowing two or more gases, each ofsaid gases having a mole fraction, through a gap interface between asubstrate mount for supporting said substrate and a heat sink; varyingthe flow rate of one or more of said gases flowing through said gapinterface to control said temperature of said growth surface of saidsubstrate to a precision of at least about ±20° C. within a temperaturerange of about 200°-2000° C.; and varying the mole fraction of one ormore of said gases flowing through said gap interface to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±20° C. within said temperature range.
 14. A method ofclaim 13 whereinsaid step of varying said flow rate further comprisesvarying the flow rate of one or more of said gases to control saidtemperature of said growth surface of said substrate to a precision ofat least about ±10° C. within said temperature range; and said step ofvarying said mole fraction further comprises varying the mole fractionof one or more of said gases to control said temperature of said growthsurface of said substrate to a precision of at least about ±10° C.within said temperature range.
 15. A method of claim 13 whereinsaid stepof varying said flow rate further comprises varying the flow rate of oneor more of said gases to control said temperature of said growth surfaceof said substrate to a precision of at least about ±5° C. within saidtemperature range; and said step of varying said mole fraction furthercomprises varying the mole fraction of one or more of said gases tocontrol said temperature of said growth surface of said substrate to aprecision of at least about ±5° C. within said temperature range.
 16. Amethod of claim 13 whereinsaid step of varying said flow rate furthercomprises varying the flow rate of one or more of said gases to controlsaid temperature of said growth surface of said substrate to a precisionof at least about ±2° C. within said temperature range; and said step ofvarying said mole fraction further comprises varying the mole fractionof one or more of said gases to control said temperature of said growthsurface of said substrate to a precision of at least about ±2° C. withinsaid temperature range.
 17. A method of claim 13 whereinsaid step ofvarying said flow rate further comprises varying the flow rate of one ormore of said gases to control said temperature of said growth surface ofsaid substrate to a precision of at least about ±1° C. within saidtemperature range; and said step of varying said mole fraction furthercomprises varying the mole fraction of one or more of said gases tocontrol said temperature of said growth surface of said substrate to aprecision of at least about ±1° C. within said temperature range.
 18. Amethod of claim 13 whereinsaid step of varying said flow rate furthercomprises varying the flow rate of one or more of said gases to controlsaid temperature of said growth surface of said substrate to a precisionof at least about ±1° C. within said temperature range in response to atemperature feedback sensor; and said step of varying said mole fractionfurther comprises varying the mole fraction of one or more of said gasesto control said temperature of said growth surface of said substrate toa precision of at least about ±1° C. within said temperature range inresponse to a temperature feedback sensor.
 19. A method for controllingthe temperature of a substrate having a growth surface during chemicalvapor deposition comprising the steps of:flowing two or more gases, eachof said gases having a mole fraction, through a gap interface between asubstrate mount for supporting said substrate and a heat sink;controlling the flow rate of one or more of said gases to control thetemperature of said growth surface of said substrate to a precision ofat least about ±20° C. within a temperature range of about 200°-2000°C.; and controlling the mole fraction of one or more of said gases tocontrol the temperature of said growth surface of said substrate to aprecision of at least about ±20° C. within a temperature range of about200°-2000° C.
 20. The method of claim 19 whereinsaid step of controllingsaid flow rate further comprises controlling said flow rate of one ormore of said gases to control the temperature of said growth surface ofsaid substrate to a precision of at least about ±10° C. within atemperature range of about 200°-2000° C.; and said step of controllingsaid mole fraction further comprises controlling said mole fraction ofone or more of said gases to control the temperature of said growthsurface of said substrate to a precision of at least about ±10° C.within a temperature range of about 200°-2000° C.
 21. The method ofclaim 19 whereinsaid step of controlling said flow rate furthercomprises controlling said flow rate of one or more of said gases tocontrol the temperature of said growth surface of said substrate to aprecision of at least about ±5° C. within a temperature range of about200°-2000° C.; and said step of controlling said mole fraction furthercomprises controlling said mole fraction of one or more of said gases tocontrol the temperature of said growth surface of said substrate to aprecision of at least about ±5° C. within a temperature range of about200°-2000° C.
 22. The method of claim 19 whereinsaid step of controllingsaid flow rate further comprises controlling said flow rate of one ormore of said gases to control the temperature of said growth surface ofsaid substrate to a precision of at least about ±2° C. within atemperature range of about 200°-2000° C.; and said step of controllingsaid mole fraction further comprises controlling said mole fraction ofone or more of said gases to control the temperature of said growthsurface of said substrate to a precision of at least about ±2° C. withina temperature range of about 200°-2000° C.
 23. The method of claim 19whereinsaid step of controlling said flow rate further comprisescontrolling said flow rate of one or more of said gases to control thetemperature of said growth surface of said substrate to a precision ofat least about ±1° C. within a temperature range of about 200°-2000° C.;and said step of controlling said mole fraction further comprisescontrolling said mole fraction of one or more of said gases to controlthe temperature of said growth surface of said substrate to a precisionof at least about ±1° C. within a temperature range of about 200°-2000°C.
 24. The method of claim 19 whereinsaid step of controlling said flowrate further comprises controlling said flow rate of one or more of saidgases to control the temperature of said growth surface of saidsubstrate to a precision of at least about ±1° C. within a temperaturerange of about 200°-2000° C. in response to a temperature feedbacksensor; and said step of controlling said mole fraction furthercomprises controlling said mole fraction of one or more of said gases tocontrol the temperature of said growth surface of said substrate to aprecision of at least about ±1° C. within a temperature range of about200°-2000° C. in response to a temperature feedback sensor.